We are developing an MHC-haploidentical allogeneic bone marrow transplantation model that parallels human treatment and can be used to decipher the immunologic impact of post-transplantation cyclophosphamide (PTCy). We are studying the impact of this therapy on clinical endpoints (survival, graft-versus-host disease, weight); accompanying these studies is a detailed characterization of the immunologic and histopathologic changes associated with this approach. Once the model is fully characterized and the mechanisms by which PTCy prevents GVHD uncovered, we will use this understanding as a basis to explore how to refine this BMT approach clinically towards the clinical goals of further reducing graft-versus-host disease, ensuring reliable engraftment with minimal conditioning, and serving as a platform for other therapies to reduce relapse. We also are exploring the impact of PTCy on human T cells in mixed lymphocyte cultures with the goal of improving our understanding of the immunologic impact of PTCy in order to improve clinical outcomes.